Demodulation circuit, a decode circuit and a digital PLL circuit for an optical disc apparatus

Abstract

An optical disc apparatus has a demodulation circuit performing an FSK demodulation by being provided with a binary signal which is obtained by binarizing a signal reproduced from an optical disc on which an FSK modulation signal is previously recorded. An edge interval of the binary signal is measured. An FSK modulation component is obtained from a difference between a measured edge interval value and a previously determined edge interval reference value. A demodulation value is obtained based on a moving average of the FSK modulation component. A moving average of the demodulation value is compared with a reference value so as to obtain a binary FSK demodulation signal. Additionally, the optical disc apparatus includes a decode circuit for decoding binary data from a biphase code signal which is reproduced from an optical disc and to be inverted at an end of each bit. When an inversion of the biphase code signal is not performed at an end of a bit, the decode circuit corrects the binary data immediately before or after the end of the bit. Further, the optical disc apparatus includes a digital PLL circuit which divides a frequency of a demodulated signal reproduced from the optical disc by a predetermined dividing ratio. A clock signal is obtained based on an edge interval value of the divided modulated signal.

What is claimed is:  
     
       1. A demodulation circuit of an optical disc apparatus performing an FSK demodulation by being provided with a binary signal which is obtained by binarizing a signal reproduced from an optical disc on which an FSK modulation signal is previously recorded, said demodulation circuit comprising: 
       edge interval measuring means for measuring an edge interval of said binary signal;  
       subtracting means for obtaining an FSK modulation component from a difference between a measured edge interval value and a previously determined edge interval reference value;  
       first moving average means for obtaining a moving average of said FSK modulation component;  
       demodulation value calculating means for obtaining a demodulation value based on an average value output from said first moving average means;  
       second moving average means for obtaining a moving average of said demodulation value; and  
       comparing means for comparing an average value output from said second moving average means with a reference value so as to obtain a binary FSK demodulation signal.  
     
     
       2. A decode circuit of an optical disc apparatus for decoding binary data from a biphase code signal which is reproduced from an optical disc and to be inverted to an end of each bit, said decode circuit comprising: 
       means for recognizing lack of bit inversion;  
       correction signal generating means for generating, when an inversion of said biphase code signal is not performed at an end of a bit, a correction signal for correcting the binary data immediately before or after said end of said bit; and  
       data correcting means for correcting the decoded binary data by using said correction signal.  
     
     
       3. An optical disc apparatus including a demodulation circuit performing an FSK demodulation by being provided with a binary signal which is obtained by binarizing a signal reproduced from an optical disc on which an FSK modulation signal is previously recorded, said demodulation circuit comprising: 
       edge interval measuring means for measuring an edge interval of said binary signal;  
       subtracting means for obtaining an FSK modulation component from a difference between a measured edge interval value and a previously determined edge interval reference value;  
       first moving average means for obtaining a moving average of said FSK modulation component;  
       demodulation value calculating means for obtaining a demodulation value based on an average value output from said first moving average means;  
       second moving average means for obtaining a moving average of said demodulation value; and  
       comparing means for comparing an average value output from said second moving average means with a reference value so as to obtain a binary FSK demodulation signal.  
     
     
       4. An optical disc apparatus including a decode circuit for decoding binary data from a biphase code signal which is reproduced from an optical disc and to be inverted to an end of each bit, said decode circuit comprising: 
       means for recognizing lack of bit inversion;  
       correction signal generating means for generating, when an inversion of said biphase code signal is not performed at an end of a bit, a correction signal for correcting the binary data immediately before or after said end of said bit; and  
       data correcting means for correcting the decoded binary data by using said correction signal.  
     
     
       5. An optical disc apparatus comprising: 
       A) a demodulation circuit performing an FSK demodulation by being provided with a binary signal which is obtained by binarizing a signal reproduced from an optical disc on which an FSK modulation signal is previously recorded, said demodulation circuit comprising:  
       edge interval measuring means for measuring an edge interval of said binary signal;  
       subtracting means for obtaining an FSK modulation component from a difference between a measured edge interval value and a previously determined edge interval reference value;  
       first moving average means for obtaining a moving average of said FSK modulation component;  
       demodulation value calculating means for obtaining a demodulation value based on an average value output from said first moving average means;  
       second moving average means for obtaining a moving average of said demodulation value; and  
       comparing means for comparing an average value output from said second moving average means with a reference value so as to obtain a binary FSK demodulation signal.  
       B) a decode circuit for decoding binary data from a biphase code signal which is reproduced from said optical disc and to be inverted at an end of each bit, said decode circuit comprising:  
       means for recognizing lack of bit inversion:  
       correction signal generating means for generating, when an inversion of said biphase code signal is not performed at an end of a bit, a correction signal for correcting the binary data immediately before or after said end of said bit; and  
       data correcting means for correcting the decoded binary data using said correction signal; and  
       C) a digital PLL circuit comprising:  
       frequency dividing means for dividing a frequency of a demodulated signal reproduced from an optical disc by a predetermined dividing ratio;  
       measuring means for measuring an edge interval of an output signal of said frequency dividing means; and  
       clock generating means for generating and outputting a clock signal based on an edge interval value obtained by said measuring means.